wake up from Power down mode

[Vonn]

Iam using uc 89c2051 with a keypad connected to one of its 2 ports , i want to save power in my design as much as i can ; so i want to work in power down mode and let the uc to wake up only if the user clicks the key ; but the problem is that " the uc wakes up from power down mode only with a hardware reset " so i need to make a tricky circuit which can do that ..
when the user clicks a key , the uc have a hardware reset and get in the loop which scan the port to get the id of the key pressed and take an action before the user left his finger out of the key ...how can i do that ?

 

[2000]

solving problem

hey pal,

Is that a matrix keypad? if so, use simply an AND port with the Columns in the input and the output should be the reset. Be careful to disable this when the uc is awaken.
regads,
2000

 

[Vonn]

OK but ..

ok but what about the power absorped in the AND logic circuit ???
I am trying to save power as much as i can so i am working in power down mode which only needs 2 micr amp. current

 

[2000]

powerdown current

sorry pal, but the datasheet I've for the AT89C2051 tells that in PD mode with 3V it consumes 20uA.... but anyway a HCMOS port would consume some current... sorry

good luck,

2000